The present invention relates to methods and products for producing increased numbers of hematopoietic cells, of restoring to preselected normal levels numbers of hematopoietic cells, to therapies for treating deficiencies in hematopoietic cells and to in vitro methodologies for culturing hematopoietic cells.
PT-100 is a dipeptide consisting of valine-prolineboronic acid (ValboroPro) designed to interact with the cell surface receptor CD26. CD26, a type II transmembrane protein is expressed on the cell surface of a number of cell types, including lymphocytes (Marguet, D. et al., Advances in Neuroimmunol. 3:209-215 (1993)), hematopoietic cells (Vivier, I. et al., J. Immunol. 147:447-454 (1991); Bristol, et al., J. Immunol. 149:367 (1992)) thymocytes (Dang, N. H. et al., J. Immunol. 147:2825-2832 (1991), Tanaka, T. et al., J. Immunol.149:481-486 (1992), Darmoul, D. et al., J. Biol. Chem.267:4824-4833 (1992)), intestinal brush border membrane and endothelial cells. Cell surface associated CD26 is a sialoglycoprotein, with most of its mass on the outside of the cell.
CD26 has been best characterized on peripheral T cells where it functions as a potent costimulatory signal for T cell activation. Its surface expression is upregulated upon T cell activation (Dong, R. P. et al., Cell 9:153-162 (1996), Torimoto, Y. et al., J. Immunol. 147:2514 (1991), Mittrucker, H-W. et al., Eur. J. Immun. 25:295-297 (1995), Hafler, D. A. et al, J. Immunol. 142:2590-2596 (1989), Dang, N. H. et al., J. Immunol. 144:409 (1990)). CD26 has also been identified in rodents as an important regulatory surface receptor in hematopoiesis and lymphoid development (Vivier, I. et al., J. Immunol. 147:447-454 (1991)). The primary structure of CD26 is highly conserved between species (Ogata, S. et al., J. Biol. Chem. 264:3596-3601(1998)). In humans CD26 seems to be involved in the regulation of thymocyte activation, differentiation and maturation (Dang, N. H. et al., J. Immunol. 147:2825-2832(1991); Kameoka, J. et al., Blood 85:1132-1137 (1995)). We have evidence that CD26 is expressed within the human and murine hematopoietic systems.
CD26 is an ectoenzyme with activity identical to that of Dipeptidyl Peptidase IV (DPP-IV), a serine type exopeptidase with high substrate specificity. It cleaves N-terminal dipeptides from proteins if the penultimate amino acid is proline, or in some cases alanine (Fleischer, B. Immunol. Today 15:180 (1994)). PT-100 is a potent inhibitor of DPP-IV activity.
The prior art PCT published application WO94/03055 teaches methods of producing increased numbers of hematopoietic cells by administering inhibitors of DPP-IV. The teaching of this published application, however, is that dosages of at least 1 mg/kg body weight are necessary to achieve such hematopoietic cell increases. This published application also teaches that inhibitors are administered to mammals which have an established deficiency of hematopoietic cells. The teaching also suggests that cytokines be administered in conjunction with the inhibitors to increase the production of hematopoietic cells in a subject.